The Darkness II

Black Holes can be found randomly on the bodies of enemies you have killed in the place of their heart and you pick them up the same way you would eat a heart. However, they will only start showing up after you have purchased the "Black Hole" Talent. Click here for information on Jackie's Talents.

Buy this Talent as soon as you are able. I found it to be reasonably helpful in the campaign. Any time you see one on a dead body be sure to throw it at someone --even if it's just one person. This achievement will come with time.

The kills needed can be accumulated over multiple playthroughs of the game.

Edit: As SIE Zaznex mentioned in the comments, if you're holding a Black Hole and a light shines on you, you will drop it and lose the chance to use it. In fact, it will even damage you if you drop it on yourself. So use it ASAP!

Edit 2: As noted by multiple people in the comments, if you still need Black Hole kills once you're done with this campaign you can try replaying the final level, "Heart of Darkness". There seems to be many more Black Holes there.

Just a quick note to say that you don't need to get it on one play through. I didn't get it first time (lots of cursing), but it popped on the first black hole I did on new game + so don't worry about it if you don't come across many black holes.

Black holes are an annoying thing to get kills with because unlike the original Darkness where it was a skill you could choose and deploy at any time, they now randomly spawn inside enemy corpses in place of their hearts. Kills are difficult to come by simply due to the random chance of a usable black hole spawning, and most later enemies can't even be sucked into them without damaging them significantly, especially on harder difficulties.

There are many things to consider for this achievement, first and foremost that reloading checkpoints does retain the kill count, though I am uncertain if dying still counts them. You must also purchase a skill named Black Hole before they even have a chance to start spawning, which ends up costing in the neighborhood of 3000 essence to unlock because you must first purchase requisite skills in the tree to unlock it (being Demon Blades, Heart Health, and Demonic Lift). In addition, I did not attempt this before purchasing the following skill, Caustic Black Hole, which increases the radius of the black hole and costs an extra 1500-ish.

As for how to gain this achievement easily, I recommend playing the mission "Q and A" on easy. At the beginning of the mission, you'll fight about a dozen guys inside of a pool hall, then approximately a half dozen on the upper floor. This requires a bit of luck, but if one of the bodies has a black hole available then you're in good shape. Make sure to destroy all the lights in the area (as walking under one will cause you to drop the black hole and lose it) then grab it and continue forward until you checkpoint. You should be facing a couple of posters labelled "Grinder" with an Exit sign above, and a door to your right.

If you exit the door and proceed, your darkling will grab a car door and there will be five enemies in cover near a car ahead. Walk past your darkling and toss the black hole with as close to the car as you can, and wait until you collect their five essences. Then simply pause and reload checkpoint, and conveniently enough, you will respawn at the door still holding the black hole. Rinse and repeat until the achievement pops.

This area is also excellent for finishing all of the other "kill X enemies with Y" achievements if you have the requisite talents unlocked. I also finished Swarm King here, and it would be ideal for Dark Akimbo, executions, demon arm kills, and gun channeling (combine them as necessary to save time, e.g. akimbo two seaparate weapons and kill the enemies with gun channeling while they're being swarmed). There are also cars along both sides of you to grab doors for thrown kills, and you can pretty easily combine everything you have to kill 5 ways for Versatile Killer (demon arm, shoot with gun, shoot with gun channeling, throw object, throw enemy, swarm, and execute, just to name seven).